#include <stdio.h>
#include <math.h>

double dist( double x1, double y1, double x2, double y2 );

int main()
{    
    double x1, y1, x2, y2;

    scanf("%lf %lf %lf %lf", &x1, &y1, &x2, &y2);
    printf("dist = %.2f\n", dist(x1, y1, x2, y2));

    return 0;
}
double dist( double x1, double y1, double x2, double y2 )
{
	double z;
	z=sqrt(pow(x1-x2,2)+pow(y1-y2,2));
	return z;
 } 
